There so far has been proposed a magnetic recording medium of double-layered structure which comprises an upper layer containing a magnetic powder and a lower layer containing a non-magnetic powder such described as in Japanese Pat. O.P.I. Pub. Nos. 187418/1988, 191315/1988, for the purpose of improving the electromagnetic conversion property of a magnetic recording medium.
However, these magnetic recording media were not primarily intended to be used as digital recording media, and, though they have the double-layered structure, the thickness of their upper layer is relatively thick; therefore, the loss in properties resulting from layer thickness and self-demagnetization becomes larger. This makes it difficult to obtain an adequate electromagnetic conversion property and running durability required of a digital recording medium.
That is, in a digital recording medium having a capability of high density recording, when high playback outputs in high frequency area are brought about by fortification of coercive force and smoothing of medium surface, playback outputs in low frequency area such as control signals become insufficient. Though playback outputs can be enhanced in both frequency areas by making the coercive force in the upper magnetic layer high and that in the lower magnetic layer low, this inevitably increases the thickness of the lower layer, causing undesired problems in overwriting property.
When the thickness of the magnetic layer is thinned and a non-magnetic layer is provided at the lower position to improve the overwriting property, other necessary properties in both high and low frequency areas are lost again. Further, improvement in high frequency properties by single use of a hexagonal barium ferrite magnetic powder brings about deterioration in low frequency property and overwriting property.
As described above, attempts to give well-balanced desirable properties to a digital recording medium do not easily succeed because of antagonism between reciprocal factors.